Substituent Effect on the Optoelectronic Properties of Poly(p-phenylenevinylene) Based Conjugated-Nonconjugated Copolymers

摘要

Two classes of light emitting Poly(p-phenylenevinylene) (PPV) based conjugated-nonconjugated copolymers (CNCPs) have been synthesized. The conjugated chromophores containing 2-methoxy-5-(20-ethylhexyloxy)- 1,4-phenylenevinylene (MEHPV) and 2,5-dimethyl- 1,4-phenylenevinylene (DMPV) moieties are rigid segments and nonconjugated portion containing hexyl units are flexible in nature. All copolymers were synthesized by wellknown Wittig reaction between the appropriate bisphosphonium salts and the dialdehyde monomers. The resulting polymers were found to be readily soluble in common organic solvents like chloroform, THF and chlorobenzene. The effect of chromophore substituents on the optical and redox properties of the copolymers has been investigated. Color tuning was carried out by varying the molar percentage of the comonomers. The UV-Vis absorption and PL emission of the copolymers were in the range 314–395 nm and 494–536 nm respectively. All the polymers show good thermal stability. Polymer light-emitting diodes (PLEDs) were fabricated in ITO/PEDOT:PSS/emitting polymer/ cathode configurations of selected polymers using doublelayer, LiF/Al cathode structure. The emission maxima of the polymers were around 499–536 nm, which is a bluegreen part of the color spectrum. The threshold voltages of the EL polymers were in the range of 5.4–6.2 V.